Phagocytosis of apoptotic cells by macrophages that were pretreated with purified IgG. A, B. Macrophages were pre-treated with IgG from SLE patients who were anti-SR-A positive (SP), anti-SRCR (anti-MARCO) positive (MP), anti-SR-A and anti-SRCR double-positive (DP), anti-SRCR and anti-SR-A double negative (DN), or IgG from healthy controls who are anti-SR-A and anti-SRCR double negative (CONTROL) before being cultured with apoptotic cells. Purified IgG were incubated with SRCR and SRA (antigen adsorbed) or not (non-antigen adsorbed) before added to interact with macrophage as described in Materials and Methods. Pre-incubation with DP reduced the percentage of macrophages ingesting apoptotic cells, resulted in a significantly higher inhibition rate of ingestion. Pre-incubation with SP, MP, and DP reduced the percentage of macrophages with apoptotic cells binding to their surface, as inhibition rates significantly increased. The inhibition rates significantly decreased when anti-SRCR and anti-SRA antibodies had been adsorbed off (all P < 0.05). An * indicates a statistically significant difference P < 0.05 by Mann-Whitney U test or paired t-test. Each bar represents the mean + SEM (n = 4). Results are representative of three experiments. C. Dose response of the IgG mediated inhibition of phagocytosis. Decreased percentage of macrophages ingesting apoptotic cells correlated with increased concentration of incubating IgG from one SLE patient positive for both anti-SRCR and anti-SR-A (P) (r = -0.943, P = 0.005). Concentration of IgG from one healthy control (control) did not correlate with the percentage of macrophages ingesting apoptotic cells (P = 0.208). Bar represents the mean ± SEM (n = 2). Results are representative of three experiments.